Sheet conveyance apparatus, image forming apparatus, and image forming system

ABSTRACT

A sheet conveyance apparatus includes a conveyance guide configured to guide a sheet along a conveyance center line extending in a conveyance direction, a reference member including an abutment surface, a conveyance unit configured to convey the sheet while abutting a first edge of the sheet against the abutment surface, a detection unit configured to detect a first angle formed between the first edge of the sheet and a second edge adjacent to the first edge, a moving unit configured to move the reference member so as to change a second angle formed between the abutment surface and the conveyance center line, and a control unit configured to perform a movement process in which the moving unit moves the reference member such that, when the first angle is referred to as α, the second angle becomes an absolute value of a difference 90 degrees minus α.

BACKGROUND OF THE INVENTION Field of the Invention

This disclosure relates to a sheet conveyance apparatus conveying asheet, and an image forming apparatus and an image forming systemprovided with same.

Description of the Related Art

Hitherto, a registration apparatus of an obliquely conveyingregistration type which conveys a sheet while abutting a side edge ofthe sheet against a reference member is suggested formed between areference edge and a non-reference edge adjacent to the reference edgeis determined using a side edge of the sheet as the reference edge.Then, based on this angle, an angle of the reference member is adjustedsuch that the deviation in margins at the reference and nonreferenceedges becomes even.

Recently, sometimes, a post-processing apparatus is coupled to an imageforming apparatus such as a printer, and the post-processing such as acutting process and a stapling process is performed in thepost-processing apparatus. At this time, an edge of the sheet is usuallyused as a processing reference in the post-processing, and, sometimes,there is a case where a reference (side edge) for the image formationand a skew correction in the image forming apparatus does not match theprocessing reference for the post-processing.

For example, in a case where, after the skew correction and the imageformation have been performed using the side edge as the reference inthe registration apparatus described in Japanese Patent Laid-Open No.2011-98790, the post-processing is performed using an edge adjacent tothe side edge as the reference in the post-processing apparatus, apositional variation of an image on the sheet after the post-processingoccurs. Therefore, especially in a case where a squareness of the sheetis low, there is a risk that the quality of the final deliverables isdegraded.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, a sheet conveyanceapparatus includes a conveyance guide configured to guide a sheet alonga conveyance center line extending in a conveyance direction, areference member including an abutment surface extending along theconveyance direction, a conveyance unit configured to convey the sheetwhile abutting a first edge of the sheet against the abutment surface ofthe reference member, a detection unit configured to detect a firstangle formed between the first edge of the sheet and a second edgeadjacent to the first edge, a moving unit configured to move thereference member so as to change a second angle formed between theabutment surface and the conveyance center line, and a control unitconfigured to perform a movement process in which the moving unit movesthe reference member such that, when the first angle is referred to asα, the second angle becomes an absolute value of a difference 90 degreesminus α.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall schematic diagram showing an image forming systemrelating to this embodiment.

FIG. 2A is a plan view showing a skew correction unit.

FIG. 2B is a plan view of the skew correction unit showing a state wherethe sheet is conveyed by an upstream conveyance portion.

FIG. 3A is a plan view of the skew correction unit showing a state wherea reference member has been pivoted.

FIG. 3B is a plan view of the skew correction unit showing a state wherethe sheet is conveyed by an obliquely conveying portion.

FIG. 4A is a plan view of the skew correction unit showing a state wherethe sheet has reached a pre-registration sensor.

FIG. 4B is a plan view of the skew correction unit showing a state wherethe sheet has been slid by a registration roller pair.

FIG. 5 is a plan view of the skew correction unit showing a state wherethe sheet has been further slid by the registration roller pair.

FIG. 6A is a diagram showing an example of the sheet and an imageposition.

FIG. 6B is a diagram showing the other example of the sheet and theimage position.

FIG. 6C is a diagram showing an error in the image position among thesheets.

FIG. 7A is a diagram for describing a method for a calculation of anangle of an abutment reference edge.

FIG. 7B is a diagram for describing a method for a calculation of anangle of a non-reference edge

FIG. 8 is a graph indicating a difference in ON timings ofpre-registration sensors.

FIG. 9A is a diagram for describing the moving velocity of theregistration roller pair.

FIG. 9B is a diagram for describing the moving velocity of theregistration roller pair.

FIG. 10 is a diagram for describing a method for a calculation of aslide correction amount of the registration roller pair.

FIG. 11 is a diagram for describing a method for calculations of anangle of the reference member and an edge position correction amount ofthe sheet in duplex printing.

FIG. 12 is a control block diagram relating to this embodiment.

FIG. 13 is a flowchart showing skew correction control.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, details of representative embodiments of this disclosurewill be described. To be noted, embodiments described below exemplarilydescribe this disclosure, and configurations, and sizes, materials,shapes, relative arrangements, the control, and the like of componentsdescribed below do not limit a scope of this disclosure unless otherwisespecifically stated.

General Arrangement

As shown in FIG. 1 , an image forming system 1 relating to thisembodiment includes an image forming apparatus 100 and a post-processingapparatus 600 coupled to the image forming apparatus 100. The imageforming apparatus 100 is a full color laser beam printer of anelectrophotographic system and an intermediate transfer tandem system.Further, the image forming apparatus 100 is a print on demand (POD)machine capable of performing printing including but not limited togeneral office use, and is able to use various kinds of sheets, servingas a recording medium, including paper such as standard paper and anenvelope, coated paper, a plastic film such as a sheet for an overheadprojector (OHT), and a cloth. The operation of the image formingapparatus 100 is controlled by a control unit 9 including, for example,an arithmetic unit such as a central processing unit (CPU), a memorysuch as a random-access memory (RAM), and a memory unit such as aread-only memory (ROM).

The image forming apparatus 100 includes an image forming unit 513, asheet feed unit 100B, and a conveyance apparatus 100D. The image formingunit 513 includes four process cartridges PY, PM, PC, and PBk formingfour colors of toner images of yellow (Y), magenta (M), cyan (C), andblack (K), and exposing units 511Y, 511M, 511C, and 511Bk. To be noted,the four process cartridges PY, PM, PC, and PBk are the same in aconfiguration except for differences in colors in which images areformed. Accordingly, only the configuration and an image forming processof the process cartridge PY will be described herein, and descriptionsof the other process cartridges PM, PC, and PBk will be omitted.

The process cartridge PY includes a photosensitive drum 508, a chargeroller, not shown, a cleaner 509, and a developing unit 510. Thephotosensitive drum 508 is constructed by coating an organicphotoconductive layer on an outer circumferential surface of an aluminumcylinder, and rotated by a drive motor, not shown. Further, anintermediate transfer belt 506 rotated by a drive roller 504 in an arrowG direction is disposed in the image forming unit 513, and wound arounda tension roller 505, the drive roller 504, and a secondary transferinner roller 503. Primary transfer rollers 507Y, 507M, 507C, and 507Bkare disposed inside of the intermediate transfer belt 506, and asecondary transfer outer roller 56 is disposed outside of theintermediate transfer belt 506 so as to face the secondary transferinner roller 503.

The sheet feed unit 100B includes a sheet storage portion 51 storing thesheet S, a lift-up unit 52 ascending and descending while stacking thesheet S, and a sheet feed portion 53 feeding the sheet S on the lift-upunit 52. While a pneumatic conveyance type pneumatically sucking andconveying the sheet S by separating the sheet into one sheet at a timeis employed in this embodiment, it is not limited to this. For example,for the sheet feed portion 53, it is acceptable to employ a rollerconveyance type conveying the sheet by a pickup roller and the like, andan electrostatic attraction type sucking and conveying the sheet byelectrostatic force.

The conveyance apparatus 100D includes a conveyance unit 54, a skewcorrection unit 55, a pre-fixing conveyance unit 57, a fixing unit 58, abranch conveyance unit 59, a reverse conveyance unit 501, and a duplexconveyance unit 502. These units each include a conveyance roller pairfor conveying the sheet. The fixing unit 58 includes a fixing nipportion 58 a for conveying the sheet by nipping.

Next, an image forming operation of the image forming apparatus 100configured as described above will be described. When an image signal isinput to the exposing unit 511Y from a personal computer, not shown, andthe like, the exposing unit 511Y irradiates a laser beam correspondingto the image signal on the photosensitive drum 508 of the processcartridge PY.

At this time, a surface of the photosensitive drum 508 has beenuniformly charged in a predetermined polarity and voltage beforehand,and an electrostatic latent image is formed on the surface by the laserbeam irradiated from the exposing unit 511Y via a mirror. Theelectrostatic latent image formed on the photosensitive drum 508 isdeveloped by the developing unit 510, and a toner image of yellow (Y) isformed on the photosensitive drum 508.

Similarly, the exposing units 511M, 511C, and 511Bk irradiate therespective photosensitive drums of the process cartridges PM, PC, andPBk with the laser beam, and toner images of magenta (M), cyan (C), andblack (K) are formed on the respective photosensitive drums. The tonerimages of the respective colors formed on the respective photosensitivedrums are transferred onto the intermediate transfer belt 506 by theprimary transfer rollers 507Y, 507M, 507C, and 507Bk. Then, by theintermediate transfer belt 506 rotated by the drive roller 504, a fullcolor toner image is conveyed to a secondary transfer nip T2 formed bythe secondary transfer inner and outer rollers 503 and 56. A tonerremained on the photosensitive drum 508 is collected by the cleaner 509.To be noted, the image forming processes of the respective colors areperformed in the timing superimposing the toner image on an upstreamtoner image primarily transferred onto the intermediate transfer belt506.

In parallel with this image forming process, the sheet S is fed from thesheet feed unit 100B, and the sheet S is conveyed to a duplex conveyancepath R of the duplex conveyance unit 502 via a conveyance path 91. Then,the sheet S passes a conveyance path 54 a of the conveyance unit 54, andis conveyed to the skew correction unit 55. The skew of the sheet S iscorrected by the skew correction unit 55, and the sheet S is conveyed tothe secondary transfer nip T2 by a registration roller pair 7 inpredetermined conveyance timing. The full color toner image on theintermediate transfer belt 506 is transferred onto a first surface(front surface) of the sheet S by a secondary transfer bias applied tothe secondary transfer outer roller 56. A remained toner remained on theintermediate transfer belt 506 is collected by a belt cleaner 2.

The sheet S onto which the toner image has been transferred is conveyedto the fixing unit 58 by the pre-fixing conveyance unit 57. Then, thesheet S is guided to the fixing nip portion 58 a of the fixing unit 58,and, by proving predetermined heat and pressure, the toner is melted andbonded (fixed). With respect to the sheet S passed through the fixingunit 58, the path selection of selecting a path between the conveyanceto the post-processing apparatus 600 and the conveyance to the reverseconveyance unit 501 is performed by the branch conveyance unit 59. To benoted, it is also possible to perform the so called facedown conveyanceconveying the sheet S such that the sheet S is conveyed to a sheetdischarge tray 500 with the sheet S inverted so as to turn the firstsurface, on which the image has been formed at the secondary transfernip T2, to the underside.

In a case where the image is formed on only one side of the sheet S, thesheet S is conveyed from the branch conveyance unit 59 to thepost-processing apparatus 600. In a case where the images are formed onboth sides of the sheet S, the sheet S is conveyed to the reverseconveyance unit 501 by the branch conveyance unit 59. Then, the sheet Sis switchbacked by the reverse conveyance unit 501. The sheet S whichhas been switchbacked is conveyed from the reverse conveyance unit 501to the duplex conveyance unit 502, and guided to the conveyance unit 54and the skew correction unit 55. Thereafter, the image is formed on asecond surface (back surface) of the sheet S at the secondary transfernip T2, and discharged to the post-processing apparatus 600.

Post-Processing Apparatus

Next, the post-processing apparatus 600 will be described in detail. Thepost-processing apparatus 600 is coupled to the image forming apparatus100, and includes a conveyance unit 601, a swing roller 603, a staplingunit 620, and a sheet discharge tray 610. The stapling unit 620 includesa process tray 602 for loading the sheet S, a regulation plate 604 forregulating a position of a trailing edge of the sheet S stacked on theprocess tray 602, and a stapler 605 for performing a stapling process onthe sheet S.

The post-processing apparatus 600 receives the sheet S from the branchconveyance unit 59 of the image forming apparatus 100, and conveys thesheet S by the conveyance unit 601. The swing roller 603 is capable ofpivoting between upper and lower positions, and positioned in the upperposition when the conveyance unit 601 discharges the sheet S to thesheet discharge tray 610. When the sheet S has been discharged to theprocess tray 602, the swing roller 603 pivots from the upper position tothe lower position.

In a case where the stapling process is not performed on the sheet S,the swing roller 603 discharges the sheet S to the sheet discharge tray610 as it is. On the other hand, in a case where the stapling process isperformed on the sheet S, the swing roller 603 conveys the sheet S onthe process tray 602 toward the regulation plate 604. Then, since thetrailing edge of the sheet S abuts against the regulation plate 604, aposition of the sheet S in a conveyance direction is regulated, and alsothe skew of the sheet S is corrected. After an alignment process asdescribed above has been performed with respect to a predeterminednumber of sheets of the sheet S, the stapler 605 performs the staplingprocess with respect to the predetermined number of sheets of the sheetS. A sheet bundle which has been provided with the stapling process isdischarged to the sheet discharge tray 610 by the swing roller 603.

Skew Correction Unit

Next, using FIGS. 2A and 2B, the skew correction unit 55 will bedescribed. As shown in FIGS. 2A and 2B, the skew correction unit 55,serving as a sheet conveyance apparatus, includes, from upstream towarddownstream in the conveyance direction F, an upstream conveyance portion41, an obliquely conveying portion 42, and a slide portion 43. To benoted, it is acceptable to include the control unit 9 in the skewcorrection unit 55. The upstream conveyance portion 41 includes anupstream conveyance guide 11, conveyance roller pairs 14 a and 14 b, acontact image sensor (CIS) sensor 101, and pre-registration sensors 102a and 102 b.

With a fixed guide 12, described later, a lower conveyance guide 13, anda movable guide 25, the upstream conveyance guide 11 constructs aconveyance guide portion 45 guiding the sheet S in the conveyancedirection F in the skew correction unit 55. The conveyance guide portion45 forms a conveyance path CP through which the sheet S passes, and aconveyance center line CT1 of the conveyance path CP, serving as aconveyance path, extends in the conveyance direction F. In thisembodiment, a center standard using the conveyance center line CT1 as areference for the conveyance of the sheet S and the image formation inthe image forming unit 513 is adopted.

The conveyance roller pair 14 b is disposed downstream of the conveyanceroller pair 14 a in the conveyance direction F, and the CIS sensor 101is disposed between the conveyance roller pairs 14 a and 14 b in theconveyance direction F. Further, the pre-registration sensors 102 a and102 b are disposed downstream of the conveyance roller pair 14 b in theconveyance direction F. The CIS sensor 101 and the pre-registrationsensors 102 a and 102 b construct a detection unit 47 detecting an angleα, described later. To be noted, in the detection unit 47, it isacceptable to include part of the control unit 9 for determining theangle α based on detection results of the respective sensors. Further,the detection unit 47 is not limited to the configuration of thisembodiment, and it is acceptable to determine the angle α by imaging thesheet, for example, by a camera and the like.

The CIS sensor 101 is disposed so as to be capable of detecting aposition of an abutment reference edge Es which is one side of the sheetS in a width direction W orthogonal to the conveyance direction F. Inparticular, by acquiring the image at fixed time intervals, the CISsensor 101 is capable of acquiring a positional change of the abutmentreference edge Es as a sequential image at the time when the sheet Spasses through a detection area of the CIS sensor 101.

The pre-registration sensors 102 a and 102 b are disposed in symmetricalpositions in the width direction W with respect to the conveyance centerline CT1. The pre-registration sensors 102 a and 102 b each output asignal of Low in a case where the sheet S is absent in a detectionposition, and output a signal of High in a case where the sheet S ispresent in the detection position. Therefore, by a switch of the signalfrom Low to High, it is possible to detect the timing when the sheet Spasses through the respective detection positions of thepre-registration sensors 102 a and 102 b.

The obliquely conveying portion 42 includes the fixed guide 12 and anobliquely conveying unit 26, and the obliquely conveying unit 26includes the movable guide 25, obliquely conveying roller pairs 24 a to24 c, and a reference member 20. The abutment reference edge Es of thesheet S is abutted against the reference member 20, and the referencemember 20 includes an abutment surface 20 a extending along theconveyance direction F. Further, the reference member 20 is pivotablearound a pivot shaft 21 as a center, and urged toward a cam 22 by anurging spring 23.

A position of the reference member 20 in a pivot direction is determinedby abutting against the cam 22, and, since the cam 22 is rotatablydriven by an angle adjustment motor 31, the reference member 20 pivotsaround the pivot shaft 21 as the center. As described above, by drivingthe angle adjustment motor 31, serving as a moving unit, it is possibleto change an angle β (refer to FIG. 3A) of the reference member 20. Theangle β, serving as a second angle, is an angle formed between theconveyance center line CT1 and the abutment surface 20 a. In otherwords, the angle β is an angle formed between the conveyance direction Fand the abutment surface 20 a.

Each of the obliquely conveying roller pairs 24 a to 24 c includes aroller pair, and a rotation shaft of at least one side of the rollerpair inclines with respect to the width direction W and the conveyancedirection F. Thereby, the sheet S is conveyed toward the abutmentsurface 20 a by the obliquely conveying roller pairs 24 a to 24 c. Thatis, the obliquely conveying roller pairs 24 a to 24 c, serving as aconveyance unit, conveys the sheet S while abutting the abutmentreference edge Es of the sheet S against the abutment surface 20 a ofthe reference member 20. Thereby, the sheet S is conveyed in a statewhere the abutment reference edge Es is in slide contact with theabutment surface 20 a, and a posture of the sheet S follows the abutmentsurface 20 a. Thus, the skew of the sheet S is corrected.

The movable guide 25, the obliquely conveying roller pairs 24 a to 24 c,and the reference member 20 of the obliquely conveying unit 26 areintegrally movable in the width direction W by a slide drive motor 32.Further, the obliquely conveying unit 26 is movable to a standbyposition Pw and a retracting position Pe in accordance with a size ofthe sheet S which is conveyed. In FIGS. 2A and 2B, the standby positionPw and the retracting position Pe are indicated by a position of theabutment surface 20 a of the reference member 20.

The obliquely conveying unit 26 moves to and waits in the standbyposition Pw before the sheet S is conveyed. The standby position Pwmeans a position in which an abutting margin Xo is added to an edgeposition Xp of the sheet S as defined by the center standard. Theabutting margin Xo is a distance for conveying the sheet S by followingthe abutment surface 20 a without colliding with an upstream end of thereference member 20 in the conveyance direction F.

Then, having delivered the sheet S to the registration roller pair 7,the obliquely conveying unit 26 moves from the standby position Pw tothe retracting position Pe. The retracting position Pe is a position inwhich a retracting distance Xe is added to the standby position Pw, andthe retracting distance Xe is a distance for retracting the referencemember 20 in the width direction W such that the reference member 20does not interfere with the conveyance of the sheet S.

As described above, the obliquely conveying unit 26 is positioned in theretracting position Pe when the sheet S is not present in the obliquelyconveying portion 42, and moves to the standby position Pw when thesheet S has entered the obliquely conveying portion 42, and returns tothe retracting position Pe again after the sheet S has been delivered tothe registration roller pair 7.

To be noted, when the obliquely conveying roller pairs 24 a to 24 cstart the skew correction of the sheet S, it is suitable that theconveyance roller pairs 14 a and 14 b do not nip the sheet S. In thisembodiment, the control unit 9 counts a predetermined time from thetiming in which the pre-registration sensors 102 a and 102 b havedetected a leading edge of the sheet. Then, the control unit 9 controlssuch that nips of the conveyance roller pairs 14 a and 14 b are releasedin the timing in which the leading edge of the sheet S reaches theobliquely conveying roller pair 24 a after the predetermined time haspassed.

The slide portion 43 includes the lower conveyance guide 13, theregistration roller pair 7, a registration drive motor 33, aregistration slide motor 34, and a pre-registration sensor 103. Theregistration roller pair 7, serving as a downstream conveyance portion,is disposed downstream of the obliquely conveying roller pairs 24 a to24 c in the conveyance direction F, and conveys the sheet S in theconveyance direction F. The pre-registration sensor 103 is disposedupstream of the registration roller pair 7 in the conveyance directionF, and, similar to the pre-registration sensors 102 a and 102 b, iscapable of detecting the timing of the sheet S passing through thedetection position.

The registration roller pair 7 is rotatable by the registration drivemotor 33, and slidable in the width direction W by the registrationslide motor 34. After the sheet S has been delivered from the obliquelyconveying roller pairs 24 a to 24 c, so as to align a position of thesheet S with an image forming position, the registration roller pair 7slides the sheet S in the width direction W in a state nipping the sheetS. A movement amount of the registration roller pair 7 in the widthdirection W at this time is the sum of the abutting margin Xo and aslide correction amount Xf, described later.

To be noted, when the registration roller pair 7 slides in the widthdirection W, it is suitable that the obliquely conveying roller pairs 24a to 24 c do not nip the sheet S. In this embodiment, the control unit 9releases nips of the obliquely conveying roller pairs 24 a to 24 c basedon the timing in which the pre-registration sensor 103 has detected thesheet S. Further, the control unit 9 releases a nip of the registrationroller pair 7 based on the timing in which the sheet S has beendelivered to the secondary transfer nip T2, and returns the registrationroller pair 7 to a standby position before a slide movement.

Variation of Image Position on Sheet due to Shape of Sheet

Next, based on FIGS. 6A to 6C, an error of an image position on thesheet due to a shape of the sheet will be described. Generally, while,in a registration type which uses a certain edge of the sheet as areference edge, it is assumed that the sheet is cut perpendicularly,actually, there is the sheet whose accuracy of a squareness is bad. Thisis because, in addition to a cause resulting from the accuracy of acutter, since fiber orientation varies inside of the sheet, there is aneffect of unevenness in a degree of expansion/contraction caused bychanges in temperature and humidity, etc.

For example, with respect to a sheet A shown in FIG. 6A and a sheet Bshown in FIG. 6B, the squarenesses and the shapes of the sheets aredifferent from each other. Then, in FIGS. 6A and 6B, an image IM isformed on the sheets A and B based on the abutment reference edge Es.

However, there is a case where a reference edge for the conveyance andthe image formation in the image forming apparatus 100 is different froma reference edge in the post-processing apparatus 600. That is, there isa case where, in the image forming apparatus 100, the image is formed onthe sheet based on the abutment reference edge Es, serving as a firstedge, and, in the post-processing apparatus 600, the post-processing isperformed based on a non-reference edge En, serving as a second edge,adjacent to the abutment reference edge Es. For example, as describedabove, having aligned the sheets by abutting the non-reference edges Enof the respective sheets against the regulation plate 604, thepost-processing apparatus 600 performs a stapling process of the sheetbundle constituted by these sheets. That is, the stapling process of thesheet bundle is performed with reference to the non-reference edge En.Hereinafter, the reference edge of the sheet S in the stapling processis referred to as a post-processing reference edge.

In this case, if the sheets A and B shown in FIGS. 6A and 6B are mixedin the sheet bundle, as shown in FIG. 6C, the image positions of therespective sheets constituting the sheet bundle vary, and the quality ofthe final printed deliverables is degraded. Therefore, in thisembodiment, in a case where the post-processing (stapling process) isperformed in the post-processing apparatus 600 with reference to thenon-reference edge En, the skew correction unit 55 is controlled suchthat the image is formed in parallel to the non-reference edge En.

To be noted, in the following, the non-reference edge En adjacent to theabutment reference edge Es is assumed to be a downstream edge in theconveyance direction F of the sheet S, namely the leading edge of sheetS. In other words, the abutment reference edge Es is an edge extendingalong the conveyance direction F of the sheet, and the non-referenceedge En is an edge extending along the width direction W orthogonal tothe conveyance direction F of the sheet. In this case, having performedthe duplex printing on the sheet S, the non-reference edge En abutsagainst the regulation plate 604, and becomes an alignment reference inthe post-processing apparatus 600.

Detection of Angle of Sheet

Next, using FIGS. 7A to 8 , a method for detecting the angle α, servingas a first angle, formed between the abutment reference edge Es and thenon-reference edge En of the sheet S will be described. To be noted,hereinafter, in a plan view, a counter-clockwise direction is expressedas a positive direction. Further, unless otherwise specifically stated,the respective angles described below are angles of a case where theconveyance center line CT1 (refer to FIG. 2A) is treated as 0 degree,namely angles with respect to the conveyance center line CT1 (refer toFIG. 2A).

As shown in FIG. 7A, an angle of the abutment reference edge Es of thesheet S is detected by the CIS sensor 101. In particular, the CIS sensor101 detects a position X1 of the abutment reference edge Es when thetime T equals T1, and a position X2 of the abutment reference edge Eswhen the time T equals T2 (which is larger than T1). Then, whenconveyance velocity in the conveyance direction F of the sheet S isreferred to as conveyance velocity Vs, the angle Θs of the abutmentreference edge Es is calculated by the following equation.

Θs=tan⁻¹{(X1−X2)/(Vs*(T2−T1))}   Equation (1)

Next, as shown in FIG. 7B, an angle of the non-reference edge En of thesheet S is detected by the pre-registration sensors 102 a and 102 b. Inparticular, in a case where the sheet S has been conveyed in a statewhere the non-reference edge En is inclined with respect to the widthdirection W, as shown in FIG. 8 , detection timings of the non-referenceedge En by the pre-registration sensors 102 a and 102 b are differentfrom each other. When the detection timings of the pre-registrationsensors 102 a and 102 b are respectively referred to as Ta and Tb and adistance between the pre-registration sensors 102 a and 102 b in thewidth direction is treated as a distance X102, the angle Θn of thenon-reference edge En is calculated by the following equation.

Θn=tan⁻¹{X102/(Vs*(Tb−Ta))}   Equation (2)

By the equations (1) and (2) above, the angle a formed between theabutment reference edge Es and the non-reference edge En is calculatedby the following equation.

α=Θs+Θn . . .   Equation (3)

Now, in a case where a is not equal to 90 degrees, if the skewcorrection of the sheet S is performed by the skew correction unit 55 ina state where the angle β of the abutment reference member is kept at 0degree, the non-reference edge En of the sheet S is inclined by thedifference α minus 90 degrees with respect to the width direction W. Ina case where the stapling process is performed in the post-processingapparatus 600 with respect to the non-reference edge En, due to theinclination of the non-reference edge En described above, the imageformed on the sheet bundle on which the stapling process has beenperformed varies. Therefore, by setting beforehand the angle β of thereference member 20 at the difference 90 degrees minus α, assuming thecounter-clockwise direction as positive, it becomes possible to form theimage in line with the non-reference edge En, so that it is possible toreduce variations in the respective images in the sheet bundle.

Moving Velocity of Registration Roller Pair

Next, using FIGS. 9A and 9B, a calculation method of a moving velocityof the registration roller pair 7 in the width direction W will bedescribed. As shown in FIGS. 9A and 9B, in a case where the angle β isnot equal to 0 degree, a travelling direction Fs of the sheet S which isbeing conveyed while abutting against the abutment surface 20 a isinclined by the angle β from the conveyance direction F. Then, when thesheet S is delivered from the obliquely conveying roller pairs 24 a to24 c to the registration roller pair 7, a difference arises between theconveyance direction F of the sheet S by the registration roller pair 7and the travelling direction Fs.

When the sheet S is delivered from the obliquely conveying roller pairs24 a to 24 c to the registration roller pair 7, even in a case where avariation arises in the conveyance of the sheet S, it is necessary tosurely deliver the sheet S. Therefore, it is common to provide a time inwhich both of the obliquely conveying roller pairs 24 a to 24 c and theregistration roller pair 7 convey the sheet S at the same time. However,if the sheet S is delivered as described above without sliding theregistration roller pair 7, due to the difference between the conveyancedirection F of the sheet S and the travelling direction Fs, a rotationalmoment Ms arises in the sheet S.

FIG. 9A shows a case where β is larger than 0 degree, and the sheet Sreceives the rotational moment Ms in the counter-clockwise directionfrom the reference member 20. FIG. 9B shows a case where β is less than0 degree, and the sheet S receives the rotational moment Ms in theclockwise direction by the conveyance force of the obliquely conveyingroller pairs 24 a to 24 c. If the sheet S receives the rotational momentMs as described above, there is a possibility of causing the skew, awrinkle, and the damage of the sheet S.

Therefore, in this embodiment, the registration roller pair 7 iscontrolled so as to receive the sheet S while being moved in the widthdirection W by the registration slide motor 34. The moving velocity Vrof the registration roller pair 7 at the time of receiving the sheet Sis calculated as described below by using the conveying velocity Vs inthe conveyance direction F of the sheet S and the angle β.

Vr=−Vs·tan β  Equation (4)

To be noted, a direction of the moving velocity Vr, as shown by an arrowFr, from a lower side of a sheet surface of FIGS. 9A and 9B toward anupper side is referred to as positive. Further, when the delivery of thesheet S to the registration roller pair 7 has been surely completed, theobliquely conveying roller pairs 24 a to 24 c release the nips.

As described above, the registration roller pair 7 of this embodiment ismoved at the velocity Vr in the width direction W (arrow Fr) whileconveying the sheet S at the conveying velocity Vs in the conveyancedirection F. Thereby, the registration roller pair 7 is able to conveythe sheet S in a direction aligned with the travelling direction Fs ofthe sheet S in the obliquely conveying portion 42, so that it ispossible to receive the sheet S without arising the rotational moment inthe sheet S. Therefore, it is possible to reduce the skew, the wrinkle,and the damage of the sheet S.

Slide Correction Amount

Next, using FIG. 10 , a calculation method of a slide correction amountof the registration roller pair 7 will be described. As described above,since a position of the sheet S delivered to the registration rollerpair 7 varies from a position of the image formation in the widthdirection W, the sheet S is slid by the registration roller pair 7 inthe width direction W.

A corrected slide amount Xr that is a distance by which the registrationroller pair 7 slides the sheet S in the width direction W is an amountin which the slide correction amount Xf is added to the abutting marginXo described above. The slide correction amount Xf corresponds to thedeviation in the width direction W arisen from obliquely conveying thesheet by the angle β with respect to the conveyance direction F in theobliquely conveying portion 42.

As shown in FIG. 10 , using a distance y1 between the pivot shaft 21 andthe pre-registration sensor 103 in the conveyance direction F, a counttime ΔTc, the conveying velocity Vs of the sheet S, and the angle α, theslide correction amount Xf is calculated as follows. To be noted, thecount time ΔTc is a time from when the pre-registration sensor 103 hasdetected the leading edge of the sheet S to when the registration rollerpair 7 starts the slide movement.

Xf=(y1+Vs·ΔTc)tan β . . .   Equation (5)

Further, the corrected slide amount Xr is expressed by the followingequation.

Xr=Xo+Xf . . .   Equation (6)

Details at Duplex Printing

Next, using FIG. 11 , calculation methods of an angle of the referencemember 20 at the time of the duplex printing and an edge positioncorrection amount Xpd in the width direction W of the sheet S will bedescribed. In a case performing the duplex printing, so as to improvethe quality of the deliverables, when the sheet S is inverted andreturned, it is necessary to control a positional relationship between asecond surface of the sheet S and the image such that positions of theimages on first and second surfaces match each other.

Since, in this embodiment, a so-called switchback method reversing theleading and trailing edges of the sheet S is employed in the caseperforming the duplex printing, a relative inclination angle between theabutment reference edge Es and the non-reference edge En is inverted.That is, with respect to the angle β of the reference member 20, whichis equal to the difference 90 degrees minus α at the time printing onthe first surface, the angle β of the reference member 20 at the timeprinting on the second surface becomes minus one, multiplied by thedifference 90 degrees minus α.

Further, since the image is formed in a state where the abutmentreference edge Es is inclined with respect to the image, at an edgewhich becomes the leading edge of the second surface (the tailing edgeof the first surface), the edge position Xp of the sheet S in the widthdirection W defined by the center standard of the image is differentfrom the first surface. An edge position correction amount Xpd that isthe difference described above is expressed by the following equationwhen the length of the sheet S in the conveyance direction F is referredto as L.

Xpd =L·tan(−(90°−α)) . . .   Equation (7)

Therefore, in the skew correction at the time of printing the secondsurface of the duplex printing, the angle β of the reference member 20,and the standby position Pw and the retracting position Pe of thereference member 20 are respectively calculated by the followingequations.

β=−(90°−α) . . .   Equation (8)

Pw=Xp+Xpd+Xo. . .   Equation (9)

Pe=Xp+Xpd+Xo+Xe . . .   Equation (10)

Control Block

FIG. 12 is a control block related to the control unit 9 of thisembodiment. As shown in FIG. 12 , the CIS sensor 101, thepre-registration sensors 102 a and 102 b, and the pre-registrationsensor 103 are coupled to an input side of the control unit 9. The angleadjustment motor 31, the slide drive motor 32, the registration drivemotor 33, and the registration slide motor 34 are coupled to an outputside of the control unit 9. Further, a memory 106 is coupled to thecontrol unit 9. To be noted, it is acceptable to incorporate the memory106 inside of the control unit 9, and dispose in any position in theimage forming system 1.

Skew Correction Control

Next, with reference to FIGS. 2A to 5 , a skew correction control by theskew correction unit 55 will be described along a flowchart shown inFIG. 13 . As shown in FIGS. 2A, 2B, and 13 , the control unit 9 detectsthe angle Θs (refer to FIG. 7A) of the abutment reference edge Es andthe angle Θn (refer to FIG. 7B) of the non-reference edge En by usingthe CIS sensor 101 and the pre-registration sensors 102 a and 102 b(STEP S1). Then, by using these angles Θs and Θn, the control unit 9calculates the angle a formed between the abutment reference edge Es andthe non-reference edge En, and an error (rotational angle) γ that is adifference of the angle α from a right angle (STEPS S2 and S3). That is,γ equals 90 degrees minus α.

Next, as shown in FIGS. 2B and 13 , the control unit 9 controls theslide drive motor 32 such that the obliquely conveying unit 26 ispositioned in the standby position Pw (STEP S4). Then, the control unit9 judges from job input information whether or not the post-processingreference edge matches the abutment reference edge Es (STEP S5).

In a case where the post-processing reference edge matches the abutmentreference edge Es (STEP S5: YES), it is not necessary to change theangle of 0 degree of the reference member 20 as it is, and, also, it isnot necessary to retract the obliquely conveying unit 26 to theretracting position Pe. That is, the abutment surface 20 a of thereference member 20 becomes parallel to the conveyance direction F.Therefore, in a case where the pre-registration sensor 103 is turned ON(STEP S14: YES) due to the passage of the sheet S, the control unit 9moves the registration roller pair 7 by the abutting margin Xo in thewidth direction W after a predetermined count (SPEP S15). Thereby, thecontrol unit 9 ends the processing.

On the other hand, in a case where the post-processing reference edgedoes not match the abutment reference edge Es (STEP S5: NO), as shown inFIG. 3 , the control unit 9 drives the angle adjustment motor 31 suchthat the angle β of the reference member 20 becomes equal to γ (STEPS6). That is, when the counter-clockwise direction around the pivotshaft 21 as a center is treated as positive, the angle β of thereference member 20 becomes 90 degrees minus α. In other words, theangle β of the reference member 20 becomes the absolute value of thedifference 90 degrees minus α. To be noted, STEP S6 is a movementprocess in which the reference member 20 is moved such that the angle βbecomes the absolute value of the difference 90 degrees minus α, andSTEP S6 is executed before the sheet S has reached the abutment surface20 a or in a state where the sheet S is abutted against the abutmentsurface 20 a.

Then, as shown in FIGS. 3B and 4A, the abutment reference edge Es isabutted against the abutment surface 20 a of the reference member 20 bythe obliquely conveying roller pairs 24 a to 24 c, so that the sheet Sis conveyed by following the abutment surface 20 a. At this time, thenon-reference edge En of the sheet S becomes parallel to the widthdirection W. To be noted, even if the non-reference edge En inclineswithin 5 degrees with respect to the width direction W, it is acceptableto consider that non-reference edge En is parallel to the widthdirection W.

Next, as shown in FIGS. 4B and 5 , the control unit 9 judges whether ornot the pre-registration sensor 103 is turned ON, that is, whether ornot the sheet S has reached the pre-registration sensor 103 (STEP S7).In a case where the pre-registration sensor 103 is turned ON (STEP S7:YES), the control unit 9 moves the registration roller pair 7 in thewidth direction W at the moving velocity Vr shown in the equation (4)above in a state where the registration roller pair 7 nips the sheet S(STEP S8). Further, the control unit 9 moves the registration rollerpair 7 by the corrected slide amount Xr shown in the equation (6) abovein the width direction W (STEP S9). That is, the registration rollerpair 7 receives the sheet S while moving in the width direction W at themoving velocity Vr which is the velocity calculated based on the angleβ.

Further, the control unit 9 controls the slide drive motor 32 such thatthe obliquely conveying unit 26 moves to the retracting position Peafter a predetermined count from the time when the pre-registrationsensor 103 is turned ON (STEP S10). Further, the control unit 9 pivotsthe reference member 20 by the angle adjustment motor 31 such that theangle β becomes equal to 0 degree (STEP S11). To be noted, it isacceptable to perform STEPS S10 and S11 in parallel with or earlier thanSTEPS S8 and S9.

Then, the control unit 9 judges whether or not the printing on thesecond surface is necessary (STEP S12). In a case where the printing onthe second surface is not necessary (STEP S12: NO), that is, in a caseof a simplex printing job, the control unit 9 ends the processing.

In a case of a duplex printing job in which the printing on the secondsurface is necessary (STEP S12: YES), in accordance with equations (8)to (10), the control unit 9 calculates a rotational angle γ, the standbyposition Pw, and the retracting position Pe, which are used when thesheet S on whose first surface the image has been formed returns to theskew correction unit 55. Then, the control unit 9 stores these in thememory 106 (STEP S13), and returns to STEP S6.

While the control unit 9 executes STEPS S6 to S11 based on therotational angle γ, the standby position Pw, and the retracting positionPe stored in the memory 106, since the STEPS S6 to S11 at the time ofprinting on the second surface are similar to the descriptions at thetime of printing on the first surface described above, descriptions willbe omitted herein. Since, after the STEPS S6 to S11 at the time ofprinting on the second surface were ended, the printing on the secondsurface has been already completed at STEP S12, STEP S12 becomes NO, andthe control unit 9 ends the processing.

To be noted, the skew correction control described above is performed oneach sheet of the job, and, for example, in a case where the sheetbundle is formed in the post-processing apparatus 600, the skewcorrection control is performed on each sheet constituting the sheetbundle. That is, in a case where the post-processing reference edge doesnot match the abutment reference edge Es, the processing of STEPS S6 toS11 is performed on each sheet constituting the sheet bundle.

As described above, the skew correction control of this embodimentincludes a first mode including STEPS S6 to S11 and a second modeincluding STEPS S14 to S15. The first mode is a mode in which thereference member 20 is moved such that the angle β becomes 90 degreesminus a before the sheet S has reached the abutment surface 20 a or in astate where the sheet S is abutted against the abutment surface 20 a.The second mode is a mode in which the reference member 20 is positionedsuch that the abutment surface 20 a becomes parallel to the conveyancedirection F before the sheet S has reached the abutment surface 20 a orin a state where the sheet S is abutted against the abutment surface 20a.

As described above, by this embodiment, even in the case where thepost-processing reference edge does not match the abutment referenceedge Es, the skew correction control is performed such that thenon-reference edge En becomes parallel to the width direction W. Since,in this state, the image is transferred onto the sheet S at thesecondary transfer nip T2, the position of the image formed on the sheetS does not vary with respect to the non-reference edge En. Therefore, ifthe post-processing such as the stapling process is performed withreference to the non-reference edge En in the post-processing apparatus600, there is not a variation of the image in the sheet bundle, so thatit is possible to improve the quality of the deliverables.

Further, since the skew correction unit 55 employs an obliquelyconveying registration method, it is possible to improve productivity,and also possible to perform the skew correction on various media suchas thin paper and cardboard. Further, since the image forming positionin the image forming unit 513 is fixed regardless of the position of thepost-processing reference edge, it is possible to improve theproductivity.

To be noted, while, in this embodiment, the skew correction unit 55 istreated as the sheet conveyance apparatus, it is acceptable to considerthe image forming apparatus 100 including the skew correction unit 55and the image forming unit 513 as the sheet conveyance apparatus.Further, it is acceptable to consider the image forming system 1including the image forming apparatus 100 and the post-processingapparatus 600 as the sheet conveyance apparatus.

Other Embodiments

To be noted, while, in this embodiment, the non-reference edge En whichbecomes the post-processing reference edge is assumed to be thedownstream edge in the conveyance direction F of the sheet S, namely theleading edge of the sheet S, it is not limited to this. For example, itis acceptable to treat an upstream edge in the conveyance direction F ofthe sheet S, namely the trailing edge Er (refer to FIG. 2A), serving asa third edge, opposite to the leading edge of the sheet S as thenon-reference edge En which becomes the post-processing reference edge.In this case, by disposing the pre-registration sensors 102 a and 102 bon a further upstream side in the conveyance direction F, it is possibleto calculate an inclination Θn of the upstream edge by a difference inthe passing timings of the trailing edge of the sheet S.

Further, it is acceptable to configure such that a user is able toarbitrarily choose the leading or trailing edge of the sheet for thepost-processing reference edge. For example, it is acceptable toconfigure such that it is possible to choose the leading or trailingedge of the sheet for the post-processing reference edge by an operationpanel of the image forming apparatus 100, an external personal computer(PC), and the like. Further, it is acceptable to configure such that theleading and trailing edges of the sheet chosen for the post-processingreference edge are automatically switched in the image forming apparatus100 in accordance with the post-processing reference edge chosen by thepost-processing apparatus 600.

Further, while, in this embodiment, whether or not the post-processingreference edge matches the abutment reference edge Es is automaticallyjudged from the job input information, it is not limited to this. Forexample, it is acceptable that the user chooses whether or not thepost-processing reference edge matches the abutment reference edge Es.Further, even in the case where the post-processing reference edge doesnot match the abutment reference edge Es, it is acceptable to configuresuch that, while not performing the control of STEPS S6 to S13 in FIG.13 , the control of STEPS S14 and S15 is performed. By turning OFF therotation control of the reference member 20 as described above, it ispossible to suppress a control load, a motor drive load, and anoperational sound.

Further, in any of the embodiments described above, the descriptions areprovided by using the image forming apparatus 100 of theelectrophotographic system, this disclosure is not limited to this. Forexample, it is possible to apply this disclosure to an image formingapparatus of an ink jet system which forms the image on the sheet byejecting a liquid ink through a nozzle. Further, the image formingapparatus 100 is not limited to a printer, but includes a copier, afacsimile, a multifunction machine, and the like.

Embodiment(s) of the present invention can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent ApplicationNo.2021-117930, filed Jul. 16, 2021, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A sheet conveyance apparatus comprising: aconveyance guide configured to guide a sheet along a conveyance centerline extending in a conveyance direction; a reference member includingan abutment surface extending along the conveyance direction; aconveyance unit configured to convey the sheet while abutting a firstedge of the sheet against the abutment surface of the reference member;a detection unit configured to detect a first angle formed between thefirst edge of the sheet and a second edge adjacent to the first edge; amoving unit configured to move the reference member so as to change asecond angle formed between the abutment surface and the conveyancecenter line; and a control unit configured to perform a movement processin which the moving unit moves the reference member such that, when thefirst angle is referred to as α, the second angle becomes an absolutevalue of a difference 90 degrees minus α.
 2. The sheet conveyanceapparatus according to claim 1, wherein the control unit is configuredto perform the movement process such that the second edge of the sheetwhich is being conveyed while abutting against the abutment surfacebecomes parallel to a width direction orthogonal to the conveyancedirection.
 3. The sheet conveyance apparatus according to claim 1,wherein the movement process is performed on each sheet constituting asheet bundle.
 4. The sheet conveyance apparatus according to claim 1,further comprising a downstream conveyance unit disposed downstream ofthe conveyance unit in the conveyance direction and configured to conveythe sheet in the conveyance direction, wherein the downstream conveyanceunit is configured to receive the sheet while moving in a widthdirection orthogonal to the conveyance direction at a velocitydetermined based on the second angle.
 5. The sheet conveyance apparatusaccording to claim 1, wherein the second edge is a leading edge or atrailing edge, in the conveyance direction, of the sheet.
 6. The sheetconveyance apparatus according to claim 1, wherein the control unitincludes a first mode and a second mode, the first mode being a mode inwhich the movement process is performed before the sheet has reached theabutment surface or in a state where the sheet is abutted against theabutment surface, the second mode being a mode in which the referencemember is positioned such that the abutment surface becomes parallel tothe conveyance direction before the sheet has reached the abutmentsurface or in the state where the sheet is abutted against the abutmentsurface.
 7. The sheet conveyance apparatus according to claim 1, whereinthe reference member is configured to pivot.
 8. The sheet conveyanceapparatus according to claim 1, wherein the first edge is an edgeextending along the conveyance direction of the sheet, and wherein thesecond edge is an edge, extending along a width direction orthogonal tothe conveyance direction, of the sheet.
 9. An image forming apparatuscomprising: a conveyance guide configured to guide a sheet along aconveyance center line extending in a conveyance direction; a referencemember including an abutment surface extending along the conveyancedirection; a conveyance unit configured to convey the sheet whileabutting a first edge of the sheet against the abutment surface of thereference member; a detection unit configured to detect a first angleformed between the first edge of the sheet and a second edge adjacent tothe first edge; a moving unit configured to move the reference member soas to change a second angle formed between the abutment surface and theconveyance center line; a control unit configured to perform a movementprocessing by which the moving unit moves the reference member suchthat, when the first angle is referred to as α, the second angle becomesan absolute value of a difference 90 degrees minus α; and an imageforming unit configured to form an image on the sheet.
 10. An imageforming system comprising: the image forming apparatus according toclaim 9; and a post processing apparatus including a regulation portionconfigured to regulate a position of the second edge or a third edgeopposite to the second edge of the sheet, the post processing apparatusbeing configured to perform processing with respect to the sheet onwhich the image has been formed by the image forming apparatus and whoseposition has been regulated by the regulation portion.